Mutations that result in constitutively active K-RAS are found in over 95% of PDACs and are believed to be an initiating event for this type of cancer. Despite the high frequency of K-RAS mutations in PDAC and other cancers, efforts to date to develop therapies directed against the oncoprotein have failed. This failure has led to a focus on the effector pathways controlled by K-RAS as possible therapeutic targets (see Project 2). Project 3 is based on an alternative strategy for inhibiting the growth of K-RAS-mutant cells, which is rooted in recent success of our group and others in identifying so-called "K-RAS synthetic lethal genes". Several such genes have been identified through RNAi screens and other strategies as being required selectively In K-RAS mutant cancer cells. However, none of these genes have been adequately examined in vivo as potential tumor maintenance genes and none have been validated in the context of P DAC. In Aim 1 of Project 3, we will use RNAi and biochemical methods to investigate the effects of inhibiting four candidate synthetic lethal genes/pathways[unreadable]STK33, TBK1, NF-{K}B, and the M2 isoform of the pyruvate kinase gene (PK-M2)[unreadable]in PDAC-derived cell lines of mouse and human origin. In Aim 2, we will create a novel mouse model of PDAC that will allow for the assessment of these and other candidate tumor maintenance genes in the context of established PDAC. Using a combination of conditional alleles controlled by two site-specific recombinases (Cre and Flp), this model will allow for conditional activation of K-RAS (with or without accompanying mutation In p53) to promote PDAC development, followed by conditional inactivation of the gene of interest. This system will be deployed first to test the consequences of inhibiting Stk33, Tbk1 or PK-M2 In established, autochthonous tumors. Additional potential tumor maintenance genes identified in this project and other projects in this PO1 will be tested In the future. In Aim 3, we will use the systems developed In Aim 1 to conduct a broader screen of candidate synthetic lethal genes that might be useful in the development of therapies for PDAC. These data will tie used to prioritize genes that will be further tested in the in vivo system developed in Aim 2.